Mil Spec: MIL-C-5541E
A process designed to remove foreign metals from the surface of stainless and corrosion resistant steels and to promote natural tendency of surface to oxidize. Does not change the appearance of the base metal. Process purifies surface and therefore improves corrosion resistance.
6.1 Passivation Treatment:
6.1.1 Stainless steel parts shall be treated in one of the following aqueous solutions and maintained within the specified temperature range for the specified time.
Nitric 1 – The solution shall contain 20 to 25 percent of nitric acid and 2.5 ± 0.5 weight percent of sodium dichromate. The parts shall be immersed for a minimum of 20 min at a temperature in the range from 50 to 55°C [120 to 130°F]
Nitric 2 – The solution shall contain 20 to 45 volume percent of nitric acid.
Nitric 3 – The solution shall contain 20 to 25 volume percent nitric acid. [120 to 140°F]
Nitric 4 – The solution shall contain 45 to 55 volume percent of nitric acid. The parts shall be immersed for a minimum of 30 minuets at a temperature in a range from 50 to 55°C [120 to 130°F]
Nitric 5 – Other combinations of temperature, time and concentration of nitric acid, with or without other chemicals, including accelerates, inhibitors or proprietary solutions, capable of producing parts that pass the specified test requirements.
1.4.1 Practice A – Water Immersion Test
1.4.2 Practice B – High Humidity Test
1.4.3 Practice C – Salt Spray Test
1.4.4 Practice D – Copper Sulfate Test
1.4.5 Practice E – Potassium Ferricyanide – Nitric Acid Test
1.4.6 Practice F – Damp Cloth Test